866
FXUS63 KGRR 042350
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
750 PM EDT Fri Sep 4 2026

.KEY MESSAGES...

- Showers and Thunderstorms This Evening

- Drying out and cooling off this Weekend

- Rain Possible Tuesday

&&

.DISCUSSION...
Issued at 318 PM EDT Fri Sep 4 2026

- Showers and Thunderstorms This Evening

The radar this afternoon shows scattered thunderstorms in an area
of isentropic ascent and moisture advection from southern
Wisconsin into southwest Lower Michigan. The convective-allowing
models such as the hi-res ARW and FV3 show the storms across
southern Wisconsin moving east-southeast this evening and
traversing the southern half of the forecast area. This is
reflected in the forecast, although tweaks may be needed of course
thanks to the inherent uncertainty in modeling convection that we
have seen the past several days.

- Drying out and cooling off this Weekend

A developing Omega block across the CONUS this weekend results as
the central U.S. heat dome is bookended by cut off lows across
the NE and NW CONUS. This lowers heights across the central Great
Lakes and allows surface high pressure to build in from the
northeast with lower temperatures and dew points and a very fine
Labor Day weekend from Saturday through Monday. In face, morning
lows on Sunday and Monday could be in the upper 40s to lower 50s
across the northern half of the forecast area.

- Rain Possible Tuesday into Wednesday

The surface high retreats east eastward by Tuesday as the Omega
block breaks down. The low across the Pacific NW kicks east and
flattens the upper high, with surface low pressure tracking across
the northern Great Lakes. Return flow of moisture and a surface
warm front should kick off some showers and thunderstorms late
Tuesday into Wednesday. Another round of storms will be possible
as a cold front moves through late Wednesday.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 750 PM EDT Fri Sep 4 2026

Last several runs of the HRRR and also this afternoon`s RRFS
models develop thunderstorm cells either vicinity or SW of AZO
and BTL between 02 and 07 Z, so have gone with prob30 thunderstorm
for now. Can`t completely rule out a rogue shower or storm cell
affecting the other TAF sites to the north and east during that
time frame. Otherwise, IFR ceilings and/or visibility become
likely after 06 Z through about 13 Z, improving to MVFR during the
late morning.

&&

.MARINE...
Issued at 318 PM EDT Fri Sep 4 2026

Showers and thunderstorms could bring brief heavy rain and gusty
winds from Grand Haven to South Haven this evening, then fair
weather with light offshore winds, generally less than 15 knots,
can be expected for Saturday through Monday. High pressure will
move east on Tuesday and winds will be on the increase, with a
Small Craft Advisory possible.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Ostuno
AVIATION...CAS
MARINE...Ostuno